1. Field of the Invention
The present invention relates to a device for decelerating sheets to be placed on a stack, especially paper or cardboard sheets, as well as a machine for sheet cutting material webs that contains a decelerating device for the sheets produced by sheet cutting.
2. Description of the Background Art
In a known manner, sheet cutting machines produce individual sheets from a material web, in particular a paper or cardboard web, by sheet cutting, with the sheets then being placed on stacks. At high operating speeds it is necessary to decelerate the individual sheets, which are transported to the stacking area by conveyor belts, prior to their placement so that no problems arise during stacking.
Known from WO 91/08974, which corresponds to U.S. Pat. No. 5,265,861, is a device of the generic type in which the deceleration device has clamping elements with rotating clamping zones located on both sides of the transport plane of the sheets, wherein the clamping zones of at least one side extend into the infeed plane at least at certain times during rotation, so that a sheet can be clamped between two clamping zones. The clamping elements are driven by a variable rotary drive such that the clamping zones are at the infeed speed of the sheets upon coming into contact therewith. The speed of the clamping zones is then reduced to the desired discharge speed of the sheets. After releasing the clamping of the sheets and before clamping the following sheets, the clamping zones are accelerated to the infeed speed of the sheets again by the variable drive.
The method described in WO 91/08974 has the advantage that it is possible to decelerate the sheets with zero velocity relative to the decelerating elements. This prevents the occurrence of undesired marking on the sheets.